The new false alarm going around Facebook claims that there is a way to see accounts that are following you secretely.

It is good to know that the "following me" claim is NOT true.
According to fact-checking site Snopes, the supposed spies are found if you go to the ''Block Users'' section under Settings.
They
are then revealed when you type in "following me" in the search field.
In actual sense, what users are getting is a list of people with the words
"following" and "me" somewhere on their profiles and not a pack of
clandestine agents.

See:

Snopes pointed out that a similar false charge
was made earlier in the year around January. That time, the ''Men in Black'' were
discovered by typing "Facebook security" in the field.
Users of the social media site have to navigate these types of hoaxes
every few months. Previous scare tactics included a "copyright claim" to
prevent losing ownership of posted content and a hacker named "Jayden
K. Smith."
For
people who do want to limit who really can see their postings, the
Facebook Help Center provides information on how to change settings.